1. Field of the Invention
The present invention relates to an improvement of a color imaging array and a color imaging device for use, for example, in a color video camera.
2. Description of the Prior Art
The color video camera picks up an image of a subject and produces a video signal comprising three different color signals, for example, green, red and blue color signals. To this end, the image picked up by the video camera must be analyzed in three different colors. One approach to this is to employ a beam-splitting optical arrangement for splitting the beam into three separated beams, and three image sensors are provided in the paths of the beams for sensing the respective colors.
The above arrangement, however, is accompanied by high manufacturing costs for the three sensors and the beam-splitting optical arrangement. Furthermore, it results in an apparatus which is bulky in size.
Then, there has been proposed a single-sensor system which uses one CCD image sensor with an attached color mosaic filter to color encode the image. When compared with a black-and-white imaging system, such a single-sensor system for sensing the color image has less resolution.
To improve the color resolution, many approaches have been made. For example, U.S. Pat. No. 3,971,065 to Bayer teaches a color imaging array shown in FIG. 1a in which green filters are located at every other element positions along horizontal and vertical directions, and red and blue filters are located in alternate horizontal lines between elements with green filter. When this color imaging array is used in combination with a signal processing device designed for effecting a so-called interlaced readout as diagrammatically shown, that is a readout is effected on odd horizontal lines of increasing line number then with even horizontal lines of increasing line number. The odd rows, consisting of only red and green samples, are read out in sequence and displayed on the odd video field, followed by a display of green and blue elements alone from the even rows on the succeeding even field. This results in a yellow-cyan hue-flicker. The Bayer's color imaging array is also discussed in IEEE Journal of Solid-State Circuits, Vol. SC-13, No. 1, February 1978 the under title "Color Imaging System Using a Single CCD Area Array".
An improved Bayer type color imaging array is shown in FIG. 1b in which the green, red and blue filters are in pairs in the vertical direction, and such pairs of green, red and blue filters are disposed in a similar alignment as that shown in FIG. 1a. In other words, the first two rows in FIG. 1b correspond to the first row in FIG. 1a, and the next two rows in FIG. 1b correspond to the second row in FIG. 1a. When this arrangement of FIG. 1b is coupled with a signal processing device effecting the interlaced readout, the video signals of green, red and blue will be included in each of the odd and even fields and, therefore, this arrangement will not result in any hue-flicker. However, the arrangement of FIG. 1b has a disadvantage in that an image reproduced using the color imaging array of FIG. 1b contains fake color, as explained below.
When an image to be picked up is, e.g., a white stripe that extends vertically along the first column of the color imaging array of FIG. 1b, such a white image will not be reproduced as a white stripe but as a cyan stripe, because the first column contains only two types of sensors (green and blue sensors) whereas three types of sensors are needed to reproduce the color white.
Similarly, when an image to be picked up is, e.g., a white stripe that extends vertically along the second column of the color imaging array of FIG. 1b, such a white image will not be reproduced as a white stripe but as a yellow stripe, because the second column contains only two types of sensors (green and red sensors).
The same disadvantage exists in other prior art color imaging arrays, such as one shown in FIG. 2, disclosed in "1981 National Convention Record of the Institute of Television Engineers of Japan" published July, 1981 on pages 111 and 112 under a title "Interline System CCD Color TV Camera" by Kazushige OOI et al; and another one shown in FIG. 3, disclosed in Japanese Laid Open Patent Application (Tokkaisho) No. 55-163971 published Dec. 20, 1980.
The prior art color imaging array shown in FIG. 2 has the first and second columns occupied only by the green and red sensors, and the third and fourth columns occupied only by the green and blue sensors. Therefore, a white image sensed by the first and second columns will be reproduced as yellow, and a white image sensed by the third and fourth column will be reproduced as cyan.
The prior art color imaging array shown in FIG. 3 has a diagonal belt DB1 occupied only by the green and blue sensors, and a diagonal belt DB2 occupied only by the green and red sensors. Therefore, a white image sensed by such belts will be reproduced as yellow or cyan.